


Head Case

by Sephypsycologist



Category: Undertale (Video Game)
Genre: Gen, Soft Vore, borrower, it's iffy but everybody ends up fine, nausea mention, safe vore, starvation mention
Language: English
Status: Completed
Published: 2019-07-31
Updated: 2019-07-31
Packaged: 2020-07-28 03:55:07
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,411
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20057605
Author URL: https://archiveofourown.org/users/Sephypsycologist/pseuds/Sephypsycologist
Summary: Horror Sans finds a guest in a place no one would think to look.





	Head Case

There was something in his head.

At first he’d just thought it was him hearing voices because of his injury again, or the general trauma of being the ultimate pacifist being forced to murder and consume people.

But it wasn’t that.

Even on his better days, when everything was closer to normal and nobody fell down…the sensation of something moving in his skull was still there.

He couldn’t catch anything, never even getting a brush on his phalanges when he would scrabble inside with his hand. Just more pain and a sort of gagging sensation. But if he moved his skull quickly, he felt whatever it was slide. It was definitely SOMETHING but he wasn’t sure what.

So now he was at an impasse. He couldn’t tell his brother about it, no. Papyrus worried about him too much as it was and if it didn’t worry him he’d still get a chewing out for letting a critter into his skull.

Nothing much he could do now except try to catch it when it inevitably ventured out.

Little traps, a mousetrap here, a sticky pad there, axe rigged to a tripwire over here and-

“BROTHER? WHAT ARE YOU DOING?”

Oh.

“heya pap. I’m tryin’ to make my own traps. Wanted to see what all the fuss was about.” He wasn’t letting the cat out of the bag just yet.

“OH!” his brother beamed at him, that painfully broken smile shining with delight, “WELL I’M VERY PLEASED TO HEAR THAT. THEY’RE VERY BASIC RIGHT NOW, BUT IF YOU ARE GENUINELY TRYING, SANS, I’M SURE YOU’LL COME UP WITH SOME GOOD ONES SOON!”

As he watched Papyrus walk away from his bedroom door, Sans felt his shoulders sink. He hated lying to Papyrus, but sometimes he just didn’t feel like there was any choice.

–

The nightmares were bad tonight.

He was trapped, black sludge holding him in place while Undyne smashed through his skull over and over and that haunting red eyed smile lurked in the distance with the dying cries of everyone he’d ever cared about…

But slowly, something broke through.

A shifting, a scrabbling and banging on the inside of his skull lifted him out of his terrifying dreams.

Per usual, he jolted upward screaming from his bed, and his door banged open instantly with Papyrus’s ragged pajama-clad self there. “WHAT IS WRONG?! DID YOU HURT YOURSELF ON TRAPS?”

“s-sorry, sorry, pap.” Sans shook as his fingers instantly curled around his dead socket, “nightmare. Just a dream…go back to sleep.”

“OH.” Papyrus looked sad, hesitant to leave but… “IF YOU’RE SURE YOU’RE OKAY, THEN. GOODNIGHT, SANS.”

“night, pap. Sorry to wake you,” Sans was so glad he’d just taken his word for it.

Before he could sleep, though, he had to look. So, wandering over to the mirror on his desk, he uncovered it and groaned at the reflection.

His eye light…ugh it was so big and ugly. So red….it had been small and white once. Too corrupt now to pull off anything white, he was sure. His soul probably pulsed this same blood-drenched red. The dry, bleached bones, covered in cracks and scratches, the most fracturing around his empty socket that….wait. The little face he’d spotted in his socket ducked out of view into the dark inside and he hissed.

“so you are there, you little rat. Come out,” but his harsh whisper did nothing.

So he shook his head around, trying to get them loose, or make them fall into the gap he knew was in the back of his skull. He’d messed around as a kid plenty of times, accidentally tossing candies in the air to catch with his mouth, only for them to land in his sockets and have to be shaken into that gap to be swallowed. He didn’t care what happened after, just wanted them out.

But no, they managed to evade his attempts even while sliding around, and then he was dizzy, so he just reached his hands in to try and get them. But the reaching and the dizzy made him gag for real and that was enough to stop.

“okay…fine…you gonna be in there? You talk. Explain yourself, body snatcher,” he gasped and panted, trying to recover as he glared at the floor of his room from the mattress.

“For real?” came the small, soft voice that tickled inside his skull.

“talk or you get more shaking and corrupted magic vomit.” Throwing up was not fun for a skeleton.

“Okay! Okay…well first of all I’m not a rat, I’m a borrower,” says the voice, quick and panicked.

He sighed, trying to calm his breath the last little bit, “and what’s a borrower when it’s at home?”

There was a small shift, near the unbroken side of his skull, “We’re about the size of a mouse animal, and we used to live in the walls of you big people’s houses. But then the food ran out and a lot of us died off. I’m the last one, as far as I know.”

“huh, so you are snack sized,” Sans muttered more to himself as he slowly laid back down to stare at the ceiling instead. “so why hide in my skull?”

“Because people don’t mess with you. And I’m easy food for anybody if I’m out there. Folks don’t mind breaking holes in their walls to get at me, but they can’t exactly break you. They fear and respect you.” They sound flat, like this is just life and facts for them. Sans is in the same boat.

“and yet I can eat you, too. just got tired of trying right now, in fact.”

They laugh humorlessly, “I noticed. But it’s safer in here than out there where I can be sniffed out.”

“I don’t have to sniff you out, though. I know you’re there, and it’s only a matter of time before I can shake you just so and you fall through that gap into my jaws.” He used his ‘threat’ voice, purring and deep and oh so slow. The one with ice flowing under it that would freeze anybody.

“I’ve already figured out how to avoid that gap, thank you,” they snark back at him. “I’m not leaving. I’d rather be here than out there.”

“you sure?” maybe sugar would lure this fly better. “my brother’d love to have someone small around. he loves cute things.”

“I saw that, too.” They sighed, “Look, I’m not coming out, and it’s late. We both need more sleep.”

Huffing, Sans turned on his side and huffed as they slid, “fine. but I’m not giving up the idea of eating you.”

There wasn’t any response, and he drifted into a thankfully dreamless sleep.

–

It was more than a little shocking, when he woke up in the morning and a very small voice inside his head said, “Good morning, Sans.”

He nearly fell back onto his bed, but caught himself, “geeze, you really know how to wake a guy up, huh? you ready to be breakfast then?” Sans reached into his socket and tried to get them, pushing so hard his wrist and shoulder were aching. Didn’t yield any results, though.

“No, and why would you want to eat me, eh? now that we’re talking, neither of us has to be so “bonely” anymore, right?” He could hear the laugh in their voice, faint but there. He wanted to smile, but didn’t.

“nice pun, you’re still food.” He bounced his head around for a while, feeling them slipping and sliding but just…never quite reaching that hole. Or his reaching hands.

Dizzy again, he growled and got dressed, “you’re lucky that hole in my dome makes me have bad equilibrium.”

“I guess so,” their response was quiet.

They didn’t talk again till he was at his station.

“So what are your hobbies besides homicide?” they quip, and Sans growls.

“you’re a pest. Shut up.”

“I’m just trying to be friendly. It’s not like I actively blame you for surviving. I’m doing the same.”

He looked up, as if rolling his eye light could let him catch a glimpse of them. “most people who stay in others’ properties pay rent. Whatcha got, small fry?”

“Nothing besides my company and you know that. Nobody’d live in someone else’s skull if they had a choice,” boy he seemed to have hit a sore spot.

“fine then. Guess we’re both broke.” He didn’t really want to talk to anybody, much less a freeloader in his head.

–

They were strong willed, Sans would give them that.

No matter how many irritated insults he threw at them about being a hobo or moocher, they always responded.

“that wasn’t a very good insult. Kinda empty-headed, huh?”

“takes one to know one, oh vacant one.”

“Well, you aren’t vacant now, are you?” Sans actually snorted at that but didn’t like that they were good at puns too. It made it hard to hate them.

Even though his empty stomach made that easier.

After a few days, though, he wasn’t…so keen on losing his pun partner.

They were irritating, sure, always talking to him and making conversation. But then they asked, “Hey, is that dog guy supposed to be here?”

Sans looked up, paying more attention to his right side now, and sure enough, Doggo was drooling and glaring at him from the trees.

“get out of here, mutt. You know I can dust you where you stand,” Sans growled, and the dog barked once, harshly, before leaving.

The both of them were silent for a while, but then Sans says softly, “that’s your rent, cupcake. You watch out for my blind side and through the back if you can, and you can talk all you want.”

A strong, warm rub against the inside of his skull made Sans shudder, but his withered soul felt a little more whole for it.

–

His tenant made knock-knock jokes on the inside of his skull.

Yes, it felt weird, and echoed a bit. But dang if it wasn’t good to actually do this again. It’d been a long time since Toriel had talked to him, especially after she found out he was killing everyone who came through no matter what. Knock knock jokes were just…well, they were pure. He’d run through all his darker ones pretty quick, and now it was the good old stock. The stuff he’d been telling since elementary school (what part of it he could remember anyway).

And they liked it. They were good to talk with, his little borrower. First easy, painless conversations he’d had for years. And he felt…something.

His chest felt different, and he didn’t get as chilled out at his station. However, even trying to put a name to this feeling hurt his head, making his empty socket burn. Nope, not going there.

Another place he didn’t go was the idea of talking to his brother about his guest.

Sure, Pap could easily get the runt out of his skull but…did he really want that anymore? It was comfortable with someone to talk to out on the job, and he’d been saved from an ambush by the canine unit more than once by their lookout in his blind spots.

No, he just…he couldn’t.

There was one problem though.

No humans had come through lately, so the rations were getting very very low. Just some jerky left, and some pre-made ‘special spaghetti’ in the fridge. And Sans slowly began to wonder what the little chatterbox was eating.

There wasn’t anything else in his head, since he shook it around every morning to see if he could make them trip up into the hole inside, so either they could feed on his magic (unlikely) or they found some morsel somewhere.

He’d be pretty pleased to be as small as them, able to eat very little at a time….

“hey, tidbit, what exactly does a borrower eat?”

They snorted, “Is that a joke?”

“nah, ‘m serious.”

“Hi serious, I’m borrower.”

He chuckled. “yeah yeah, i walked into that one.”

“Surprised you don’t walk into anything else with how empty it is up here.”

“empty head, empty stomach, I’m pretty much a vacuum at this point,” Sans smirked as he rested on his arms. “but you’re a voice in my head. So does that make you my conscience or my delusion?”

“Neither. I’m that voice that tells you do to stupid things,” they giggled.

Heheh, yeah, that sounded about right.

–

Just to be sure…Sans didn’t want to believe this but he had to know.

He dipped both ends of their big slab of jerky (the last of it, and he hoped the next human would drop soon) in green food coloring. The stuff isn’t edible alone, not in that quantity, and honestly Pap uses it mostly to paint in the snow. This would tell him.

When the borrower asked why he did that, he replied, “cause I wanna prank my bro. he’ll think it’s mold at first.” And that was true. That’s why he picked green and not blue or yellow. But it wasn’t the whole truth.

Now he waited.

Few days, sure, all good. He joked with the little snack and the jerky was untouched besides the small slivers his brother and him would break off.

And then when he checked, one late evening, a corner of the green bit was gone.

The fiery rage that blazed in his soul was indescribable. Sans barely was able to keep his mouth shut long enough to make it out of town and into the deep forest before he screamed, “you’re stealing our food!”

He thrashed his head around and heard the borrower scream, but he didn’t care, “you’re taking it! we’re in a famine, you pest!”

“I have to live, too!” the little thief squealed as they were thrown about, “and I eat a mouthful every three days! How is that tiny amount even going to help you if I didn’t?!”

“You think that matters?” Sans hissed, looking around for something to stick inside his head to either stab them or fish them out, “You’ve done something unforgivable and you think you living matters?”

The anger in their tiny voice turned to sobs as he started shaking his head again, “Sans, I don’t WANT to take your food but I have no choice! I’m too small to hunt, too small to even leave your skull without being trampled, eaten, or frozen to death! Please listen to me.”

Growling in fury, he grabbed a pile of snow and shoved it into the break in his skull. Spluttering and suddenly cold, the borrower was pushed against the side of his skull near his socket, and Sans was able to reach in and yank them out, grin wide and unhinged as he finally got a good look at them. Pointed ears and a flicking tail. Heh.

“if you’re so intent on staying with me, let’s make it permanent,” he started cackling before shoving the terrified borrower in his mouth and swallowing. Oh that hurt. They were cold and struggling, and not nearly slicked enough for their ragged clothes not to stick and scrape along his throat, but he couldn’t help giggling after he slurped up the last of their tail.

The giggle turned into full on screeching laughter, before cutting off with a sound like he’d had his throat cut when their body started sliding into his stomach. Oh geeze, it’d been a long long time before he had more than a few mouthfuls of food, much less something as big as the borrower, so the stretching was painful.

Starting to pant from the sting, he tipped his head back and let the snow fall out, then sat down gingerly and pulled up the stained shirt under his hoodie. His magic was stretched thin and dark maroon, blood-like and tight against his spine. That was definitely different last time he saw it. Last time…years ago, it’d been blue, soft and round instead of the sunken film now clinging between his bones.

It had gone opaque already, system instantly wanting whatever had filled it, but he muffles a cry of pain as he sees the borrower’s fighting start as the wave of pain hits him hard. Their struggles are very easily seen with how very thin the membrane of magic around them was, how tight it was stretched over them, and the ferocity of their kicks and punches.

The sensation was sickening, literally, and he stifled a nauseous hiccup as he got to his feet, bones rattling slightly from the sharp stabs of agony from his fighting meal. Sans had to lean on the trees all the way home, but he made it well enough.

They were really making a fuss, but just knowing and feeling that something was in his belly was enough to make up for it. Really, how long had he gone without just so his brother would be happy with him? be happy with what they could give to the folks left in Snowdin?

But even now, flat on his back in bed, warm from the pain, he couldn’t sleep it off.

Hard to sleep when you can hear someone screaming at you.

“Sans, please!” their voice was quivering with fear and tears, cracking with exhaustion from the continuing fight for their life.

And then the pain started in his chest.

This pain was worse, searing and enough to set the skeleton squirming in his filthy covers. The stomach pain, yeah, that was normal, that was expected and bearable, but this was coming from his soul. His very being was burning like a hot coal lodged under his ribs.

On top of all that, the nausea was growing, leaving him swallowing despite his dry mouth, feeling like something thick was at the back of his throat.

Ugh, how long was this going to go on?

–

He had no idea how long he stayed like that, writhing at every throb from his soul and trying desperately not to lose control of his gag reflex.

The pleading hurt worse, as it sent a new wave of burning through his soul, and…that’s when it hit him.

As angry as he was they were taking food, as frustrated and hungry as he was, no part of him actually wanted the borrower to die. The humans he killed were irredeemable after…well, after that one he couldn’t remember left them here to die, but the borrower had done everything to try and be his friend, even as he attempted to eat them, even as he tried to push them away.

It was good to be full, but it hurt so bad as his soul rejected the energy his body was attempting to convert for him, making an endless feedback loop that just got worse over time.

They were tired now, just crying and begging, and finally he couldn’t stand it anymore. Hand to his mouth, Sans let his instincts go and hacked, shaking as he heaved them out of his protesting body and let them splat into his palm.

A few coughs, some gags, and then he was back in control of his body again, weak and dizzy from the energy it took that he didn’t actually have in the first place. They stared up at him, covered in the black slime of his corroded magic and staring up in confusion, frozen in place.

Sighing through his nose, Sans stuck them back in the crack in his head, “felt too empty.”

They were quiet for a while, then came that weird nuzzling inside his skull and soft hiccupping laughs, “Thank you. I won’t take anything again.”

“don’t be stupid. You’re taking breaths right now,” he replied as he started rummaging through his drawers and piles of clothes. When he found stray scraps of fabric, he slid them into his skull, “and I’ve been a shitty landlord, so I’m doing some upkeep. Don’t want a mooch-cicle in my head.”

The borrower laughed louder, clearer, and the pain in his soul finally began to fade. “laugh all you want now, tidbit. You still have to meet my brother.”

“about time. you’ve kept that cool guy in the dark long enough,” they seemed to be tired now. Sans couldn’t blame them. “but maybe later.”

Now that he thought about it, yeah. It was turn in time for everyone.


End file.
